Parallel Converter Carrier Wave Synchronization
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Solution Overview
Problem
High frequency circulating harmonic currents between converters in power systems, such as solar and wind power systems, cause stress on power semiconductor devices and cables, and existing solutions like current limiting reactors increase costs and compromise reliability.
Innovation Solution
A power system with control units that measure phase currents, determine harmonic currents, and adjust the switching cycles of carrier waves to synchronize converters, reducing the need for high-speed communication networks and high inductance reactors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If current limiting reactors with high inductance value are connected to each converter, then circulating current is limited, but cost and footprint of the power system increase
Solution Approach 1:
The invention extracts the circulating current limitation function from individual converter-level components (reactors) and implements it at the system level through control units that measure and analyze current harmonics across the parallel converter network, eliminating the need for bulky reactors at each converter
Solution Approach 2:
The invention replaces the mechanical/electrical solution of current limiting reactors with a control-based electronic solution using control units that measure phase currents, determine harmonic currents, and adjust switching cycles to synchronize carrier waves, thereby limiting circulating current without physical reactors
2Object-generated harmful factors
If high speed communication network is used to couple converters, then circulating current is limited, but reliability of the power system is compromised
Solution Approach 1:
Each control unit independently measures its own phase currents and determines harmonic currents locally, then adjusts its own switching cycles based on its own measurements and the measured circulating current, eliminating the need for high-speed communication between converters
Solution Approach 2:
The invention uses the measured phase currents and harmonic current analysis as intermediaries to coordinate the switching cycles of parallel converters without requiring direct high-speed communication links between them, thereby maintaining system reliability
3Device complexity
If converters operate without carrier wave synchronization, then system complexity is reduced, but high frequency circulating harmonic currents increase causing stress on devices
Solution Approach 1:
The control units continuously measure phase currents, determine harmonic current components, and use this feedback to dynamically adjust the switching cycles of carrier waves to achieve synchronization and minimize circulating harmonic currents
Solution Approach 2:
The invention changes the switching cycle parameters of the carrier waves dynamically based on measured harmonic currents, adjusting the time-period of switching cycles to synchronize carrier waves and reduce circulating currents
Data Source
AI summary
A power system is presented. The power system includes a first converter including a first output terminal a first control unit coupled to the first converter, a second converter including a second output terminal, where the second converter is coupled in parallel to the first converter, and a second control unit coupled to the second converter. The second control unit is configured to measure a plurality of phase currents at the second output terminal, determine a harmonic current transmitted by the second converter based on single phase current of the plurality of measured phase currents, and change a time-period of at least one switching cycle of a carrier wave of the second converter based on the determined harmonic current to synchronize with a carrier wave of the first converter.